Christian leader Michel Aoun greets his supporters as he arrives to deliver a speech during a 2015 rally near the empty presidential palace Beirut.
Photograph: Hassan Ammar/AP

Lebanon is on the verge of electing a close ally of Iran-backed Hezbollah as president, days after the nuclear deal between the west and Tehran which leaders vowed would herald a resurgent Iranian voice in the region.

The endorsement of Michel Aoun, a former general and foe-turned-ally of the Syrian regime, comes after a nearly two-year standoff that has paralysed decision-making in Beirut and despite Saudi Arabia wanting his arch-rival Samir Geagea to take the post.

Geagea has instead yielded to Aoun in a move that is now likely to anchor Iran’s influence in Lebanon.

Perennially unstable and dependent on patrons throughout its short history, Lebanon has become a major front in the ongoing Riyadh-Tehran feud, with both sides investing billions of dollars to support their respective candidates.

“I announce General Michel Aoun’s candidacy for the presidency of the republic,” Geagea said at a festive joint press conference. “I call on our allies to endorse Aoun’s candidacy.”

Aoun’s candidacy would need to be approved by a parliamentary majority, a result that appears within reach if Christian and Shia blocs can come together, along with MPs representing smaller sects.

The Saudi-backed “March 14” bloc, which accounts for most of the country’s Sunnis, and which is strongly supported by Riyadh, remained bitterly opposed to the deal until it was announced by both men on Monday night, and Geagea may face difficulties convincing them to back Aoun.

Aoun has enthusiastically supported Iran’s role in the region and his election would mark an extension of Tehran’s influence at a time when an ongoing tussle for power and influence saw Saudi Arabia sever diplomatic relations in the lead-up to the nuclear deal.

This flare-up in tensions was precipitated by an attack on the Saudi embassy in Tehran, which had followed the execution of a senior Saudi Shia cleric. However, it underscores a much broader standoff that has festered particularly since the start of the Syrian civil war and the war in Yemen, both of which have sectarian dimensions.

Saudi Arabia has largely projected its power through Lebanon’s exiled former prime minister Saad Hariri. Late last year, he put forward a compromise candidate, Suleiman Franjieh, who is closely linked to the Syrian regime, in an attempt to break a deadlock which had crippled basic services and destabilised the country.

Former Lebanese prime minister Saad Hariri speaks during a ceremony to mark the tenth anniversary of the assassination of his father Rafik Hariri, in Beirut. Photograph: Hussein Malla/AP

The move worked, but not with the result Hariri had wanted. Aoun and Geagea have been enemies since both were generals in rival Christian camps during the Lebanese civil war between 1975 and 1990, but the one person they dislike more than each other was Franjieh.

If Aoun is elected leader, as is increasingly expected, it would likely damage the March 14 bloc’s status within Lebanon, and possibly be seen as another blow to Sunni standing in the region.

Saudi officials fear Iran will use some of the windfall from the lifting of international sanctions in the wake of its nuclear deal to prop up its regional proxies, including Hezbollah, which has been directly backed by Tehran since it was founded more than three decades ago.

Saudi concerns also extend to Baghdad and Damascus. Iranian-backed Shia militias have grown more powerful and influential than the national Iraqi army, and have until recently taken the lead in the fight against Islamic State, while Iran has forcefully intervened to rescue the Syrian regime of Bashar al-Assad.

In Yemen, Saudi Arabia launched a military campaign after accusing Iran of backing rebels who overthrew the Riyadh-backed government.

Yemeni rescuers search for victims under the rubble of a police headquarters after the building was struck overnight by Saudi-led air strikes on 18 January in the rebel-controlled Yemeni capital Sanaa. Photograph: Mohammed Huwais/AFP/Getty Images

Lebanon has long been paralysed by the divided loyalties of its political elites. The country’s parliament has failed to elect a president, by law a Christian Maronite, more than 30 times, in sessions that often faileven to achieve quorum.

The country’s political dysfunction descended into farce last summer, when the government failed to negotiate a deal over new landfills, leaving rubbish piling up in the streets of Beirut, and prompting demonstrations protesting official corruption.